Nonstoichiometric Phases in the MS-M<sub>2</sub>S<sub>3</sub> Sulfide Systems

Flahaut, Jean; Domange, Louis; Patrie, Madeleine; Bostsarron, Anne-Marie; Guittard, M.

doi:10.1021/ba-1964-0039.ch016

Cited by 30 publications

(31 citation statements)

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“…[32] While the structure of the new Ta 2 N 3 and U 2 S 3 display the same topology as Sb 2 S 3 , the gap in bond lengths between the three shortest cation-anion distances and the remaining distances is not as pronounced as in the structure of Sb 2 S 3 . Following the systematics of Flahaut for relevant sulfides, selenides and tellurides of rare earths, [33] this novel tantalum nitride having U 2 S 3 structure is denoted hereafter as h-Ta 2 N 3 . The shortest Ta-N distances in h-Ta 2 N 3 are 1.91(5) and 2.04(5) Å for Ta (1) and Ta (2), respectively ( (2), then the second prism face is also capped, and the cation coordination can be described as 7 þ 1.…”

Section: Full Papermentioning

confidence: 99%

High‐Pressure Synthesis of Tantalum Nitride Having Orthorhombic U₂S₃ Structure

Zerr

Miehe

et al. 2009

Adv Funct Materials

102

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Among binary compounds, there is a high potential for discovery of novel members (polymorphic phases or compounds) of the nitrides of transition metals group due to a pronounced dependence of the oxidation state of the metals (M) on pressure. The power of high pressure–high temperature (HP‐HT) route for synthesis of binary nitrides has already been demonstrated by the discovery of cubic nitrides of the group 4 and 14 elements, of crystalline polymorphs of P3N5, and by reports on formation of four noble metal nitrides. It is anticipated that such HP products exhibit, in addition to enhanced elastic and mechanical behavior, other functional properties making them interesting for industrial applications. Here, HP–HT synthesis research is extended to nitrides of group 5 elements, resulting in the discovery of a novel hard tantalum nitride, exhibiting U2S3 structure: η‐Ta2N3 (Pbnm, a = 8.1911(17) Å, b = 8.1830(17) Å, c = 2.9823(3) Å). The stoichiometry is supported by two independent means, verifying that η‐Ta2N3 is the first thermodynamically stable transition metal nitride with a N:M ratio exceeding 4:3. Due to its high hardness and peculiar texture (needle‐like and granular crystallites), η‐Ta2N3 may find practical applications as a hard fracture resistant material.

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Section: Full Papermentioning

confidence: 99%

High‐Pressure Synthesis of Tantalum Nitride Having Orthorhombic U₂S₃ Structure

Zerr

Miehe

et al. 2009

Adv Funct Materials

102

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“…The wavenumber measurements (^1 cm~1) were calibrated using plasma lines. 3 ), unit cell, lattice constants a \ 3.9959 (3) and Ó c \ 6.8751 (8) [V \ 95.067 (14) c/a ratio of 1.7205 Ó Ó 3 ], and mean density of 6.01. It was shown that the cerium and oxygen atoms form pseudo-hexagonal prismatic cages bicapped by two sulfur atoms, as illusCe 6 O 6 trated in Fig.…”

Section: Pulverulentmentioning

confidence: 99%

Structure and bondings in cerium oxysulfide compounds. I—Electronic, infrared and resonance Raman spectra of Ce2.0O2.5S

Sourisseau

Cavagnat

Mauricot

et al. 1997

J. Raman Spectrosc.

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As a Ðrst stage, the electronic (350-900 nm), infrared and Raman (700-10 cm-1) spectra of polycrystalline samples of the oxysulÐde compound were investigated and tentative vibrational assignments are proCe 2.0 O 2.5 S posed from a comparison with the simpler parent compound. Great changes in the vibrational patterns Ce 2 O 2 S demonstrate that the two oxysulÐdes are not isostructural and that the oxidized form cannot be described as a Ce3'-containing peroxide or superoxide system. As a second stage, the resonance Raman spectra of Ce 2.0 O 2.5 S were recorded within the contour of the Ðrst electronic transitions (650-450 nm) on the absorption edge. The Raman excitation proÐles maximize at near 490 nm and exhibit large enhancements for most of the vibrational modes, in particular the higher wavenumber mCe-O equatorial stretching modes at 584 and 548 cm-1. This shows that the resonant electronic transition is more likely an excitonic type and involves a large electronic delocalization, particularly over the cerium-oxygen bonds in the equatorial planes. In conclusion, the compound does Ce 2.0 O 2.5 S not look like as a mixed-valence sample with distinct Ce3' and Ce4' constituent ions, Class II in DayÏs notation, as already known in it is better described as a Ce4'-containing broadband semiconductor in which Ce 4 O 4 S 3 ; low-energy excitonic-type transitions implying the intermediate 4f levels have to be considered and in which valences do not appear to be Ðrmly trapped.

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“…The second composition is similar to that known for other heavy RE polysulfides [5,8,9]. The third one is doubtful, as it hardly can be reached at the conditions used [10]. The full structural analysis was performed for two crystals.…”

Section: Introductionmentioning

confidence: 68%